The kind of muddy waters often seen around the Great Barrier Reef increase disease rates in fish and damage their gills, according to reef scientists.
A new study by James Cook University researchers simulated the levels of suspended sediment frequently found in the reef due to floods, coastal agriculture and industry, and dredging for ports.
The researchers, working in the Australian Research Council centre of excellence for coral reef studies, say the damaging effects from such conditions are a growing problem in coastal waters worldwide and highlight the need for continued protection of the crucial habitats.
A study co-author, Amelia Wenger, said fish were a key part of the habitat that had until now been largely overlooked in discussions of the health of the reef and its potential stressors.
Previously fish haven’t really been part of this conversation and I think they need to be because they’re obviously a huge part of the Great Barrier Reef, she said.
This research underscores the necessity for future coastal developments to consider the adverse effects of sediment on fish and reef ecosystems.
Wenger said the study was part of a growing body of literature that is showing the strong effects of sediment on fish but the first physiological assessment of the gills and bacteria component.
It comes after a damning report from Queensland’s auditor general last week raised doubts about touted improvements in reef water quality because of a lack of empirical measurement of sites.
Environmental lawyers in Australia and the US have also called for quantitative measures of reef health in a report that also claims the UN draft ruling against listing the reef in danger failed to recognise its own criteria.
The James Cook researchers said exposure to sediment was particularly acute for juvenile reef fish who swam in open waters before settling in a chosen reef. Damage to their gills interfered with their ability to source great amounts of oxygen at a critical stage of their development.
Another co-author, Jodie Rummer, said fish gills were the first line of defence in the animal’s immune response, which makes them the perfect place to look for damage associated with sediment.
Plus, harm to this vital organ affects every activity in the animal’s body that requires oxygen, Rummer said.
The lead author, Sybille Hess, said the simulated study found gills in larval clownfish exposed to sediment were congested, exhibiting twice as much mucus [as] what could be found in clean-water exposed fish.
Sediment-exposed fish also increased the number of protective cells on their gills, presumably safeguarding the delicate tissue from the damage that sediment particles could cause.
The study also found gills of affected fish harboured disease-causing bacteria.
The fourth co-author, Tracy Ainsworth, said: The presence of bacteria linked to fish disease on the gills of sediment-exposed fish suggests that exposure to, and accumulation of sediment, may trigger the development of fish diseases.
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